This proposal describes experiments aimed at understanding the control of gene expression in nerve cells. Previously isolated and characterized neuropeptide genes expressed in subsets of neurons in the Aplysia abdominal ganglion will be used as a model system. In vitro recombinants will be constructed between the bacterial structural genes B-galactosidase (B-gal) or chloramphenicol acetyl transferase (CAT) and the neuropeptide gene promoters including CIS controlling elements. The hybrid genes will then be microinjected into Aplysia neurons in organ culture and expression of the B-gal or CAT enzymes assessed. A variety of neurons which normally do or do not express the endogenous gene will be investigated in order to ascertain the cellular specificity of the expression of microinjected genes. In vitro mutations including deletions and substitutions will be constructed and the specificity of expression reassessed thus defining CIS acting elements regulating expression of the genes. We will further investigate expression of the microinjected neuropeptide genes in different physiological states. The effects of electrical activity and excitatory or inhibitory neurotransmitters will be studied. In vitro mutagenesis will again be used to define CIS acting DNA elements responsible for responding to alternate physiological conditions. Potential intracellular messengers which mediate the responses will be investigated. Among these candidate messengers are cAMP, calcium and other ions. The studies described above will define molecular genetic mechanisms utilized by the brain during development and will also help generate an understanding of neuroplasticity at the molecular genetic level. This research will further our understanding of diverse neuronal disorders ranging from learning disabilities in children to Alzheimer's disease in the aged.